Vibration detector



Aug. 22, 1933.

H. C. HAYES VIBRATION DETECTOR 2 Sheets-Shet 1 Original Filed Sept. 23,1927 HARVEY C. HA YES IN VEN TOR WQW A 7' F'ORNE Y Aug. .22, 1933. H.c1, H Y 1,923,088

VIBRATION DETECTOR OriginalFiled Sept. 23, 1927 2 Sheets-Sheet 2 HARVEYc. HAYES INVENTVOR W Ma M A TT ORNE Y PatentedAu g'. 22, 1933 1,923,088vmnA'rroN DETECTOR Harvey C. Hayes, Washington, D. C.

=riglnal application September 23, 1927, Serial No. 221,520. Divided andthis application December 8, 1930., Serial No. 500,841

3 Claims. (or. 177-352) (Granted under the Actof March 3, 1883, asamended April 30, 1928; 370 0. G. 157) range of direction. This is quiteimportant where the precise direction from which the vibration emanatesis not known and where it is desired to take note of the magnitude ofthe vibrations received.

While the device contemplated by the present invention is not limited touse in solid ground, but can be used for the reception of sound wavesthrough water or directly through the air, it is particularly wellsuited for the reception of earth tremors and thelike. One instance ofthe use to which the detector of the present invention can be put is forthe reception of waves artificially set up in the ground, as by theexplosion of a charge of dynamite, so that the character of the wavesmay be readily studied. It is well known they are directly received orreceived after refraction or reflection.

An object of the invention has been to construct a device for thepurposes specified in such a way that the mechanical energy of the soundor similar wave may readily be converted into electrical energy. Thisconversion, furthermore,

40 has been brought about without sacrificing any of the inherentcharacteristics of the original wave so that the records produced by theelectrical means will give an accurate'indication of the nature of theoriginal waves.

It has been an object to provide a very. intimate contact between thedevice and the earth "whose vibrations it is designed to detect. Forthis .purpose the outer casing of the instrument has been formed in theshape of a cone having a gradual taper and being of suflicient dimensionto insure its movement with the earth. To aid in providing this movementwith the earth, furthermore, the casing has been constructed of suitablematerial and of appropriate thickness so that the device will havesubstantially the same average density and the samecenter of gravity asthe earth into which it is inserted.

In the operation of the device which is based upon the generalprinciples of magneto-electrical devices the casing is adapted topartake of the vibrations to be recorded while an inertia member withinthe casing remains substantially sta tionary. This provides thenecessary relative movement between certain magnetic poles and adjacentmagnetic conductors to create the de- 55 sired variations in the fluxpassing through suitable coils located in the magnetic field. It is anobject to so arrange the magnets and coils that the efiects will becombined and will be substantially uniform over a wide rangeof-direction of ,70 reception.

The invention also contemplates a modification whereby the device may bemade to detect both horizontal and vertical vibrations, or suchcomponents of waves coming from any direction between the horizontal andvertical planes.

With these and other incidental objects in view one form of theinvention will now be described with reference to the accompanyingdrawings which form a part hereof and in which Figure 1 is a crosssectional view in elevation of the assembled vibration detector.

Figure 2 is a sectional view along the line 2-2 of Figure 1 with certainparts broken away to disclose others: v

Figure 3 is a diagrammatic view of the circuits employed in the use ofthe device.

Figure 4 is a vertical section through the armture and laminated ring ofa modification adapted to detect both horizontal and vertical com-'ponents of a vibration.

Figure 5 is a plan view of the parts shown Figure 4. a j

Figure 6 illustrates suitable connections for detecting both horizontaland vertical=components by means of the construction shown in Figures 4and 5.

Referring now to Figure 1 it will be noted that the main body of thedevice is formed by a conical casing 10 of any suitable material,preferably such .that with'other parts, as will be explained, it willcreate a masshaving an average density substantially the same as thatnormally encountered in surface soil. Aluminum has been found verysatisfactory for this purpose. In. practice it has been found desirableto make this casing of considerable length, approximately 30 inches overall, and the average thickness of the wall is preferably between M; andinch. For

. a distance of afew inches from the lower tip of 11 near the uppersurface of the cone.

the cone it is substantially solid, except for an opening 11 which isdrilled through this lower portion. Above the substantially solid partthere is a large cavity or openingpractically in the form of a frustrumof a cone which leaves only a wall of the desired thickness, suchasmentioned. The cone preferably tapers from a relatively sharp'point toan outside diameter in the neighborhood of five inches while the openingis approximately three" inches in diameter at the top. a

In order to facilitate the insertion of the cone into the earth it isprovided with a steel point 12 having a, screw threaded extension 13adapted to be fitted into a screw threaded opening at the lower end ofthe conical casing. The outer surlower wall of the casing.

.A resilient rod 14 of suflicientlength to have a low natural frequencyof vibration and made of any suitable material, preferably brass,carries a screw threaded tip 15 which is also adapted to fit into athreaded portion at the lower end of the conical casing; -The rodextends upwardly through the opening 11 and into the larger cavity'ofthe cone to a point substantially at or This rod is adapted to supportan armature 16 which, as shown, is preferably formed as a cross toprovide four separate pole pieces. The armature, which is preferablymadeof laminated steel such as is commonly used in transformers, may besecured in any way to the-end of the rod, as by fittingit over the endof the rod onto a shoulder formed thereon and by holding it in place bya nut as shown. On each of the four poles of the armature there ismounted a coil 1'7 formed of a suitable number of turns of insulatedwire, these coils being signated as 1, 2, 3 and 4 in Figure 4 of thedrawings. The turns or windings of the coils are arranged in such senseabout-the armature poles that current passed through them from a D. C.source will tend to establish like magv ,netic poles at opposite ends ofthe cross, for ex- 1 ample coils 1 and 4 may establish south poles,

while coils 2 and 3 may establish north poles. Suitable connecting wiresare employed to couple the coils, as shown in Figure 3. Thus coils 1 and2 are connected in series by means of their outermost turns, while coils3 and 4.are similarly connected. The inner ends of coils 2 and 3 areconnected and suitable leads are taken off from the loose ends of coils1- and 4 and from the inner end of the coil 2, these leads beingdesignated 13, 19 and 20, respectively. Insulating plate 21 made of'anysuitable material, such as bakelite, carriesjja set of three contactpoints 22 to which the several leads 18, 19 and 20 are ,connected.

Surrounding the armature there is provided an annular ring 23 made p oflaminations similar to those employed in the armature itself.

These may or may not be bound together, as desired threaded into theupper end of the casing is preferably made of some non-magneticmaterial, such as brass. It is quite essential that considerableaccuracy be provided in the fitting of the armature within the annularring. For this reason priate length which serve to support thepreviously mentioned bakelite plate 21, the lower ends of these screwsbeing fitted into threaded openings in the ring 25. i

A cap 27, preferably formed of aluminum, is adapted to enclose theelements located at the upper end of the cone and is secured to thelatter. For this purpose the cap is provided with a flange through whicha series of bolts 28, pass into a corresponding flange 29 of the cone.An annular rib 30 formed on the lower surface of the cap and having itslower edge out at an angle, as shown, is adapted to fit into an annularrecess 31 in the upper end of the cone to provide a. water-tight seal atthis point. As an aid to the effectiveness of this seal the annularrecess is preferably filled with some yielding material, such as rubber,to form a gasket. A small opening in the upper .end of the cap isadapted to permit the passage of the cable 32 having three leads 33which are connectedtoithe contact points 22. In order to provide awater-tight connection surrounding the cable the latter fits as tightlyas possible in the opening in the cap and there is also provided astufling box or gland construction in the upper portion of the cap.-Thus a small reduced portion of the latter is closed 011 by a disk 34which is supported from the top 'of the cap by a series of three bolts35. The chamber thus provided may be filled with any suitable material,such as rubber.

In practice the device if used in solid ground must be-inserted into theearth for-the full length of the cone, which, as previously stated, maybe about thirty inches. Since it would probably damage the instrument toattempt to force it directly into anyvery solid ground it is contemthelatter, in its packed condition, will be read- 1 ily transmitted to thecasing. The armature 16, however, due to its inertia will tend to remainstationary on the upper end of the rod 14 thereby tending to decreasethe air gap between certain of the poles and the annular ring 23 and atthe same time increase the air gap between one 9r more of the remainingpoles and the ring. This variation in the air gaps will, of course,tendto vary the flux passing through the several coils and will tend toinduce an E. M. F. in each of them.

In Figure 3 there is shown diagrammatically the connections which havebeen found most satisfactory in the use of the detector for thereception of earth vibrations. In this view 3'7 designates a D. C.source of current which is connected in parallel with the two pairs ofcoils, namely, 1 and 2 in one branch of the circuit and .3 and 4 in theother branch. The circuit' through the (soils 1 and 2 may be returnedthrough the sectidu 38 oftheprimary winding of a transform er, while thecircuit through the coils 3 and 4' the secondary winding of thetransformer. (However, when a relative movement is produced between thearmature and the annular ring, for example in the direction indicated bythe arrow,

the flux through coils 1 and 2 will be decreased due to the enlargementof the air gap and a current will, therefore, be induced in these coilswhich will be in the same sense as the current from the source 37, Thisadded current may pass through the coil 38 in the direction indicat-- edby the. arrow 41. At the same time the flux through the coils 3 and 4will be increased and a current opposing that supplied by the source 37will be induced and'this current, therefore, or change in current willhave the general direction in coil-39, as indicated by the arrow 42.Thus it will be seen that the two induced currents in the coils 1 and 2'and the coils 3 and 4, respectively, will be added in their eflfect inpassing through the primary of the transformer, so that a current equalto the combined effect will be induced in the secondary. winding 40. Anysuitable means may be provided for creating a visible or audibleindication of the current changes in the transformer. I A feature to benoted in connection with the generation of the induced current in themanner specified is that the precise direction from which the vibrationis received is not material, the magnitude hi the effect produced in thetransformerwill be substantially the same for a given magnitudeofvibration over a wide range of di-- rection from which it may bereceived. This is brought about by the fact that the currents induced ineach coil of a pair will be added to the current induced in the othercoil of the pair.

Considering the coils 1 and 2, for example, a vibration received in ahorizontal direction, as shown, will induce a maximum, current in coil 2and ractically, no current in cell 1. On the other ban a movement in thevertical direction, as shown, will induce a maximum current in coil 1and little or no current in coil 2. If the vibration is received fromany intermediate direction within the range between the horizontal andvertical it will generate a current in both coils corresponding to thehorizontal and; vertical components of'the motion and the two currentsin the coils 1 and 2 will be added. There is only a single definitedirection from which a vibration will have no efiect upon thetransformer This is a vibration substantially at right angles to thearrow shown in Figure 3. It will be seen that a vibration in thisdirection, say toward the upper left hand corner of the drawing, willincrease the flux in coil 2 and correspondingly decrease-the flux incoil 1 so that the two E. M. 'Ffs induced will be opposed andlpresumablyequal. Similarly the two E. M. Ffs lnduced in coils 3,,and 4 will beopposed and pre- -sumably equal so that the net eifect will be zero. Forany other direction of vibration there will at least be an eflfect equalto the difference between the horizontal and vertical components I and,as already pointed out, for any vibration within 45 of thedirectionindicat'ed by the arrow the effect of. the two components willbe added ratherthan subtracted. If desired an arrow may be placed on thecap of the instrument to correspond to the arrow on the diagram in-'-dicating the quadrant of its greatest sensitivity. In practice then thisarrow should preferably be pointed in the known or assumed direction ofthe source of the wave. Reflected or refracted waves which it may alsobe desired to detect willin all probability fall within 45 of eitherside of this direction.

After the device has been used to pick up the desired waves at aparticular location the instrument maybe pulled out of the ground. Toaid in this operation the upper end of the cone is provided with a pairof ears 43 and 44 each of which ll p ovided with an eye bolt 45. It willbe found that due to-the intimate contact of the cone with the earthconsiderable pulling will be required to remove the instrument. Theturning of the cone by forcing against one or both of the ears will aidin loosening it or a crow bar may be inserted below one of the ears topry it up. When once loosened, the instrument may be readily raised bymeans of the eye bolts.

If the device is'to be used for the reception of sound or similar wavesthrough water it is merely necessary to suspend the instrument by meansof the eye bolts in such a way as to completely immerse the device.-.The instrument is entirely water-proof sothat there is no danger ofadecting the operation in any detrimental way. a

While the construction of the device, with respect to the mounting ofthe armature and the laminated ring, previously discussed, will permitof detecting vibrations to a certain extent in both the vertical and thehorizontal directions, this form is particularly suited for thehorizontal type of vibration and is not very well suited for detectingvibrations of the vertical type. Figures 4 and 5 illustrate amodification whereby the device may be rendered equally suited to thedetection of horizontal and vertical vibrations. In this form of theinvention the cooperating faces of the armature 46 and of the annularlaminated ring 47 are formed at an angle of 45 and the armature and ringmay then be located in the, same plane, as indicated in Figure 4, withaportion of the arms of the cross overlapping a portion of the laminatedThe supporting 125 rod, similar to 14 of Figure 1, will preferably be ofless diameter and will yield slightly to the weight of the armature.Vibrations received from directly below the device will then cause thecasing, together with the ring. 4'7, to rise slightly while the armature46, due to its inertia, will remain substantially stationary so that theair gapwill be reduced and the flux passing through all of the coilswill be increased. 0n the other hand, if the vibration is received froma horizontal direction the cross will rock toward one side or the otherand thereby decrease the air gap between one or more of the poles andthe ring 47 and increase the airgap between one or more of the remainingpoles and the 1m annular ring.

Figure 6 illustrates one particular arrangement of circuits fordetecting the vibrations received ineither vertical or horizontaldirections; it will, of course, also be aflected by the two components145 of vibrations coming from any direction. For this purpose only twoof the coils say, for example, 1 and 2, will be directly employed andthe remaining coils 3 and 4 will be present only for the purpose ofbalancing the armature; cross. 150 The connection is such that the twocoils are in will, therefore, result and a' corresponding current willbe induced in the secondary and may be inglicated by any suitable means,such as the galvanometer 49.

In connection with the form of the invention, as h greinabove described,it is highly desirable to attain as nearly aspossiblethe condition inwhich the casing and all of the parts which move directly therewith,form a mass not only having an average density equal to that of thedisplaced soil but onewhose center of gravity is the same as that of thesoil displaced. It will be apparent that the more nearly this conditionis approached the more accurately the vibrations of the surroundingearth will be reproduced. Furthermore, it is desirable that the averagedensity for each increment of length shall be substantially the same.Thus,'for' example, itis preferable,

although it is practically impossible to carry it out precisely, to havethe center of gravity of each horizontal section of the device of say aninch in height in coincidence with the center of gravity of the soilwhich occupied the same space. Adherence as closely as possible to thiscondition will avoid much of the distortion in the vibrations of thecasing which would otherwise result.

While an admirable form or embodiment of the present invention has beendisclosed in detail in the foregoing sections,'it will he understoodthat many other changes may be made within the contemplation of'theinvention and which will fall within the scope of the claims whichfollow.

The invention described herein may be manufactured and used by or forthe Government of the United Statesof America for Governmental purposeswithout the payment to me of any royalty thereon.

What I' claim is:

1. In a vibration detector an elongated (3915-. ing adapted tobesupported-in the earth in a vertical pgsition, a magnetic ring securedtherein in a horizontal position, an armature mounted within said ringand having pole pieces slightly spaced from said ring and cooperatingtherewith, the cooperating faces of saidring and pole pieces beingparallel and beveled, at an acute angle with respect to the longitudinalaxis of said cas- -ing coils on said armature, means for electricallyenergizing said coils to produce a flux between said ring and said polepieces, means for supporting said armature and adapted to permit bothlongitudinal and transverse movement with respect to said casing andmeans for indicating the variation in flux through said coils due tomovements of either type.

2. In a vibration detector an elongated casing adapted to be supportedin the earth in a vertical position, a ring of magnetic material securedin said casing in a horizontal position, an armature mounted within saidring and having pole pieces spaced slightly from said ring andcooperating therewith, the faces of said pole pieces and the inner edgeof said ring being beveled at an angle of substantially 45 degrees. tothe longitudinal axis of saidcasing with said beveled faces closelyadjacent and parallel to each other, coils on said armature, means forelectrically energizing said coils to produce a flux across the spacebetween said ring and said pole pieces, means for supporting saidarmature and adapted to permit both longitudinal and transverse movementof said armature with respect to said magnetic ring, andcmeans forindicating the variations of flux through said coils due to movements ofeither type.

3. In a vibration detector an elongated casing adapted to be supported,in the earth in a vertical position,'a ring of magnetic materialsecured in said casing in a horizontal position, an armature mountedwithin said ring and having pole pieces mounted in close proximity tobut slightly spaced from said ring, the faces of said pole pieces andthe inner edge of said ring being parallel and bevelled at an angle ofsubstantially 45 degrees to the vertical axis of said casing, coils onsaid armature, a source of direct current electricity, connections"between said source of electricity and said coils so that said coilswill be energized to produce a flux between said pole pieces and saidring, means for supporting said armature comprising a rod secured at itsupper end to said armature and at its lower end to said casing, said rodbeing formed of a slightly yielding material so as to permit bothlongitudinal andtransverse movement of said armature with respect tosaid ring when said casing is vibrated, and means for indicating thevariations of flux through said coils due to movements of either type.

HARVEY C. HAYES.

